This invention relates to rotary machinery and, in particular, to apparatus for use in a rotary machine having an inner and outer casing which maintains the inner casing centered in respect to the machine shaft as the casings grow under differential thermal and/or pressure loading.
It has been found advantageous in rotary machines, such as turbines and compressors experiencing high internal pressures and temperatures, to provide the machine with both an inner casing and an outer casing. In assembly, the stationary components of the machine are generally suspended from the inner casing and the casing axially aligned with the rotor structure supporting the movable machine components. A heavier outer casing, in turn, is placed over the inner casing so that an annular space is provided therebetween. Under operating conditions, the space between the two casings is pressurized. In the case of a compressor, the space between the casings is normally pressurized to the machine discharge pressure by simply bleeding discharge fluids into this area. The casings are arranged so that the inner casing is firmly fitted within the outer casing.
When operating at high pressures and high transient temperatures, the outer casing of the machine grows at a different rate than the inner casing whereby the outer casing normally tends to move away from the inner casing. Because the rotor shaft generally extends axially through the machine, the two casings cannot be mutually supported about their commonly shared axis to maintain coaxial alignment during periods of growth. As can be seen, uncontrolled growth of the two casings can lead to misalignment of the machine components and ultimately to machine failure.